The goals of this research are to understand the nature of developmental determinants in early embryos of Caenorhabditis elegans and to elucidate the mechanisms by which these determinants become localized in the fertilized egg and the manner in which they control subsequent gene expression. We shall employ a combined genetic, biochemical, and ultrastructural approach to extend the evidence for localization of determinants in Caenorhabditis embryos, develop assays for the partitioning of developmental potential and specific macromolecules in early cleavages, identify lethal maternal-effect mutants in which abnormal partitioning leads to blocks in early embryogenesis, and investigate these mutants for clues to the nature, localization mechanism, and function of developmental determinants.